The present invention relates to a fiber structure-electrode framework of metallized plastic fibers having welded-on, current-conducting lugs.
For connecting fiber structure-electrode frameworks of metallized plastic fibers, for example, of nickel-plated polyolefin-felt or -fleece material, it is known to slot the edge of the electrode framework, to slide the current-conducting lug into this slot and then to weld together the electrode framework with the current conducting lug. However, such a possibility is very expensive and is realizable only with small quantities. With larger quantities, the current-conducting lug is placed on the galvanically reinforced edge of the fiber structure-electrode framework and is welded together with the same under pressure. The current-conducting lug thereby consists of a correspondingly shaped sheet metal member, especially of nickel or of nickel-plated sheet metal parts. During the welding of the lugs with the fiber structure-electrode framework, the bottom edge of the current-conducting lug is pressed into the metallized fiber framework, as a result of which a strong compression of the metallized fiber structure-electrode framework takes place over the reinforced edge. This will lead to cracks in the metallized electrode framework within the area of the weld and to a small supporting cross section. This all leads to a low strength of the welded connection and therewith to rejection during the further processing of the refilled fiber structure-electrodes, for example, during the mechanical impregnating, the welding of plate sets, the separating and the forming. Furthermore, the capacity of completed batteries suffers if during the operation an insufficient welded connection exists at individual plates which with an alternating load will not withstand the occurring forces and moments.
The present invention is concerned with the task to provide a fiber structure-electrode framework of metallized plastic fibers with reinforced edge and with welded-on current-conducting lug, in which no crack formation occurs in the fiber structure-electrode framework in direct proximity of the welded connection and in which the welded connection exhibits a high strength not only under tensional loads, but also in the cross direction and which makes it possible to manufacture electrodes with favorable electrical transition resistances and great lengths of life so that the same can also be used in traction batteries.
The underlying problems are solved according to the present invention in that the current-conducting lug is provided with an essentially steplessly terminating chamfer at the side abutting at the fiber framework, which forms an angle of 10.degree. to 50.degree. with the lug, in that the welding of the fiber framework is undertaken essentially on the non-chamfered part of the current-conducting lug up to 5 mm. above the beginning of the chamfer, and in that the fiber framework is compressed within the area of the welding seam and starting from the welding seam runs out on both sides approximately continuously to the full thickness. The current-conducting lug is thus provided on the side abutting at the fiber framework with an essentially steplessly terminating chamfer which forms an angle of 10.degree. to 50.degree.. The welding of the fiber framework lies essentially up to 5 mm. above the beginning of the chamfer on the non-chamfered part of the current-conducting lug. As a strong heating of the lug as well as of the fiber framework takes place during the welding, the welding in some cases may extend into the area of the chamfer. During the welding, the fiber framework is permanently compressed within the area of the welding seam by the contact pressure of the welding electrodes. This compressing takes place above all in the reinforced edge of the fiber structure-electrode framework which has mechanically a higher stability than the rest of the electrode framework. The galvanic reinforcement of the edge is known and is achieved by a greater metal deposit on the fibers of the electrode framework (DE-PS No. 31 42 091). Starting from the welding seam, a tapering to the full thickness of the fiber framework which is approximately symmetrical on both sides, is then achieved conditioned by the chamfer as well as by a corresponding construction of the counter electrode. As a result thereof, stresses in the electrode framework are far-reachingly avoided. This is particularly favorable for thicker electrode frameworks, especially those with a thickness of 1.5 to 8 mm. Metallized plastic fiber frameworks, especially felts, needle felts, fleeces and the like are used as electrode frameworks. The metallization takes place according to the conventional techniques whereby in particular nickel or copper is used as metallic coating on the fibers. The electrode frameworks are provided at the edge, where the current-conducting lug is to be attached, with an edge reinforcement which is achieved by a thicker metal coating on the individual fibers. The plastic materials suitable also for textile fibers, for example, polyolefins, polyamides, polyacrylnitriles, etc. are suitable as material for the fibers of the electrode framework, insofar as they are stable with respect to the electrolytes with which they come subsequently into contact.